1. Field of the Invention
The field of the invention relates to a surgical device and method. More particularly, it relates to a tissue ablation device assembly and method using a circumferential ablation member in combination with a position monitoring assembly in order to position the circumferential ablation member along a circumferential region of tissue at a location where a pulmonary vein extends from a left atrium.
2. Description of Related Art
Many local energy delivery devices and methods have been developed for treating the various abnormal tissue conditions in the body, and particularly for treating abnormal tissue along body space walls which define various body spaces in the body. For example, various devices have been disclosed with the primary purpose of treating or recanalizing atherosclerotic vessels with localized energy delivery. Several prior devices and methods combine energy delivery assemblies in combination with cardiovascular stent devices in order to locally deliver energy to tissue in order to maintain patency in diseased lumens such as blood vessels. Endometriosis, another abnormal wall tissue condition which is associated with the endometrial cavity and is characterized by dangerously proliferative uterine wall tissue along the surface of the endometrial cavity, has also been treated by local energy delivery devices and methods. Several other devices and methods have also been disclosed which use catheter-based heat sources for the intended purpose of inducing thrombosis and controlling hemorrhaging within certain body lumens such as vessels. Detailed examples of local energy delivery devices and related procedures such as those of the types described above are disclosed in the following references: U.S. Pat. No. 4,672,962 to Hershenson; U.S. Pat. No. 4,676,258 to InoKuchi et al.; U.S. Pat. No. 4,790,311 to Ruiz; U.S. Pat. No. 4,807,620 to Strul et al.; U.S. Pat. No. 4,998,933 to Eggers et al.; U.S. Pat. No. 5,035,694 to Kasprzyk et al.; U.S. Pat. No. 5,190,540 to Lee; U.S. Pat. No. 5,226,430 to Spears et al.; and U.S. Pat. No. 5,292,321 to Lee; U.S. Pat. No. 5,449,380 to Chin; U.S. Pat. No. 5,505,730 to Edwards; U.S. Pat. No. 5,558,672 to Edwards et al.; and U.S. Pat. No. 5,562,720 to Stern et al.; U.S. Pat. No. 4,449,528 to Auth et al.; U.S. Pat. No. 4,522,205 to Taylor et al.; and U.S. Pat. No. 4,662,368 to Hussein et al.; U.S. Pat. No. 5,078,736 to Behl; and U.S. Pat. No. 5,178,618 to Kandarpa.
Other prior devices and methods electrically couple fluid to an ablation element during local energy delivery for treatment of abnormal tissues. Some such devices couple the fluid to the ablation element for the primary purpose of controlling the temperature of the element during the energy delivery. Other such devices couple the fluid more directly to the tissue-device interface either as another temperature control mechanism or in certain other known applications as a carrier or medium for the localized energy delivery. Detailed examples of ablation devices which use fluid to assist in electrically coupling electrodes to tissue are disclosed in the following references: U.S. Pat. No. 5,348,554 to Imran et al.; U.S. Pat. No. 5,423,811 to Imran et al.; U.S. Pat. No. 5,505,730 to Edwards; U.S. Pat. No. 5,545,161 to Imran et al.; U.S. Pat. No. 5,558,672 to Edwards et al.; U.S. Pat. No. 5,569,241 to Edwards; U.S. Pat. No. 5,575,788 to Baker et al.; U.S. Pat. No. 5,658,278 to Imran et al.; U.S. Pat. No. 5,688,267 to Panescu et al.; U.S. Pat. No. 5,697,927 to Imran et al.; U.S. Pat. No. 5,722,403 to McGee et al.; U.S. Pat. No. 5,769,846; and PCT Patent Application Publication No. WO 97/32525 to Pomeranz et al.; and PCT Patent Application Publication No. WO 98/02201 to Pomeranz et al.
Atrial Fibrillation
Cardiac arrhythmias, and atrial fibrillation in particular, persist as common and dangerous medical aliments associated with abnormal cardiac chamber wall tissue, and are often observed in elderly patients. In patients with cardiac arrhythmia, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue in patients with sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction is known to occur at various regions of the heart, such as, for example, in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmia, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. In the alternative or in addition to the multiwavelet reentrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion. Cardiac arrhythmias, including atrial fibrillation, may be generally detected using the global technique of an electrocardiogram (EKG). More sensitive procedures of mapping the specific conduction along the cardiac chambers have also been disclosed, such as, for example, in U.S. Pat. No. 4,641,649 to Walinsky et al. and in PCT Patent Application Publication No. WO 96/32897 to Desai.
A host of clinical conditions can result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. In fact, atrial fibrillation is believed to be a significant cause of cerebral stroke, wherein the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle which thereafter pumps the embolism into the cerebral circulation where a stroke results. Accordingly, numerous procedures for treating atrial arrhythmias have been developed, including pharmacological, surgical, and catheter ablation procedures.
Several pharmacological approaches intended to remedy or otherwise treat atrial arrhythmias have been disclosed, such as, for example, those approaches disclosed in the following references: U.S. Pat. No. 4,673,563 to Berne et al.; U.S. Pat. No. 4,569,801 to Molloy et al.; and xe2x80x9cCurrent Management of Arrhythmiasxe2x80x9d (1991) by Hindricks, et al. Such pharmacological solutions, however, are not generally believed to be entirely effective in many cases, and are even believed in some cases to result in proarrhythmia and long term inefficacy.
Several surgical approaches have also been developed with the intention of treating atrial fibrillation. One particular example is known as the xe2x80x9cmaze procedure,xe2x80x9d as is disclosed by Cox, J. L. et al. in xe2x80x9cThe surgical treatment of atrial fibrillation. I. Summaryxe2x80x9d Thoracic and Cardiovascular Surgery 101(3), pp. 402-405 (1991); and also by Cox, J L in xe2x80x9cThe surgical treatment of atrial fibrillation. IV. Surgical Techniquexe2x80x9d, Thoracic and Cardiovascular Surgery 101(4), pp. 584-592 (1991). In general, the xe2x80x9cmazexe2x80x9d procedure is designed to relieve atrial arrhythmia by restoring effective atrial systole and sinus node control through a prescribed pattern of incisions about the tissue wall. In the early clinical experiences reported, the xe2x80x9cmazexe2x80x9d procedure included surgical incisions in both the right and the left atrial chambers. However, more recent reports predict that the surgical xe2x80x9cmazexe2x80x9d procedure may be substantially efficacious when performed only in the left atrium. See Sueda et al., xe2x80x9cSimple Left Atrial Procedure for Chronic Atrial Fibrillation Associated With Mitral Valve Diseasexe2x80x9d (1996).
The xe2x80x9cmaze procedurexe2x80x9d as performed in the left atrium generally includes forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the region of the inferior pulmonary veins en route. An additional horizontal line also connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the arrhythmogenic conduction from the boxed region of the pulmonary veins to the rest of the atrium by creating conduction blocks within the aberrant electrical conduction pathways. Other variations or modifications of this specific pattern just described have also been disclosed, all sharing the primary purpose of isolating known or suspected regions of arrhythmogenic origin or propagation along the atrial wall.
While the xe2x80x9cmazexe2x80x9d procedure and its variations as reported by Dr. Cox and others have met some success in treating patients with atrial arrhythmia, its highly invasive methodology is believed to be prohibitive in most cases. However, these procedures have provided a guiding principle that electrically isolating faulty cardiac tissue may successfully prevent atrial arrhythmia, and particularly atrial fibrillation caused by arrhythmogenic conduction arising from the region of the pulmonary veins.
Less invasive catheter-based approaches to treat atrial fibrillation have been disclosed which implement cardiac tissue ablation for terminating arrhythmogenic conduction in the atria. Examples of such catheter-based devices and treatment methods have generally targeted atrial segmentation with ablation catheter devices and methods adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers. Some specifically disclosed approaches provide specific ablation elements which are linear over a defined length intended to engage the tissue for creating the linear lesion. Other disclosed approaches provide shaped or steerable guiding sheaths, or sheaths within sheaths, for the intended purpose of directing tip ablation catheters toward the posterior left atrial wall such that sequential ablations along the predetermined path of tissue may create the desired lesion. In addition, various energy delivery modalities have been disclosed for forming atrial wall lesions, and include use of microwave, laser, ultrasound, thermal conduction, and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall.
Detailed examples of ablation device assemblies and methods for creating lesions along an atrial wall are disclosed in the following U.S. Patent references: U.S. Pat. No. 4,898,591 to Jang et al.; U.S. Pat. No. 5,104,393 to Isner et al.; U.S. Pat. Nos. 5,427,119; 5,487,385 to Avitall; U.S. Pat. No. 5,497,119 to Swartz et al.; U.S. Pat. No. 5,545,193 to Fleischman et al.; U.S. Pat. No. 5,549,661 to Kordis et al.; U.S. Pat. No. 5,575,810 to Swanson et al.; U.S. Pat. No. 5,564,440 to Swartz et al.; U.S. Pat. No. 5,592,609 to Swanson et al.; U.S. Pat. No. 5,575,766 to Swartz et al.; U.S. Pat. No. 5,582,609 to Swanson; U.S. Pat. No. 5,617,854 to Munsif; U.S. Pat. No 5,687,723 to Avitall; U.S. Pat. No. 5,702,438 to Avitall. Other examples of such ablation devices and methods are disclosed in the following PCT Patent Application Publication Nos.: WO 93/20767 to Stern et al.; WO 94/21165 to Kordis et al.; WO 96/10961 to Fleischman et al.; WO 96/26675 to Klein et al.; and WO 97/37607 to Schaer. Additional examples of such ablation devices and methods are disclosed in the following published articles: xe2x80x9cPhysics and Engineering of Transcatheter Tissue Ablationxe2x80x9d. Avitall et al., Journal of American College of Cardiology, Volume 22, No. 3:921-932 (1993); and xe2x80x9cRight and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillation,xe2x80x9d Haissaguerre, et al., Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996).
In addition to those known assemblies summarized above, additional tissue ablation device assemblies have been recently developed for the specific purpose of ensuring firm contact and consistent positioning of a linear ablation element along a length of tissue by anchoring the element at least at one predetermined location along that length, such as in order to form a xe2x80x9cmazexe2x80x9d-type lesion pattern in the left atrium. One example of such assemblies is that disclosed in U.S. Pat. No. 5,971,983, issued Oct. 26, 1999, which is hereby incorporated by reference. The assembly includes an anchor at each of two ends of a linear ablation element in order to secure those ends to each of two predetermined locations along a left atrial wall, such as at two adjacent pulmonary veins, so that tissue may be ablated along the length of tissue extending therebetween.
In addition to attempting atrial wall segmentation with long linear lesions for treating atrial arrhythmia, other ablation device and method have also been disclosed which are intended to use expandable members such as balloons to ablate cardiac tissue. Some such devices have been disclosed primarily for use in ablating tissue wall regions along the cardiac chambers. Other devices and methods have been disclosed for treating abnormal conduction of the left-sided accessory pathways, and in particular associated with xe2x80x9cWolff-Parkinson-Whitexe2x80x9d syndromexe2x80x94various such disclosures use a balloon for ablating from within a region of an associated coronary sinus adjacent to the desired cardiac tissue to ablate. Further more detailed examples of devices and methods such as of the types just described are variously disclosed in the following published references: Fram et al., in xe2x80x9cFeasibility of RF Powered Thermal Balloon Ablation of Atrioventricular Bypass Tracts via the Coronary Sinus: In vivo Canine Studies,xe2x80x9d PACE, Vol. 18, p 1518-1530 (1995); xe2x80x9cLong-term effects of percutaneous laser balloon ablation from the canine coronary sinusxe2x80x9d, Schuger CD et al., Circulation (1992) 86:947-954; and xe2x80x9cPercutaneous laser balloon coagulation of accessory pathwaysxe2x80x9d, McMath L P et al., Diagn Ther Cardiovasc Interven 1991; 1425:165-171.
Arrhythmias Originating from Foci in Pulmonary Veins
Various modes of atrial fibrillation have also been observed to be focal in nature, caused by the rapid and repetitive firing of an isolated center within cardiac muscle tissue associated with the atrium. Such foci may act as either a trigger of atrial fibrillatory paroxysmal or may even sustain the fibrillation. Various disclosures have suggested that focal atrial arrhythmia often originates from at least one tissue region along one or more of the pulmonary veins of the left atrium, and even more particularly in the superior pulmonary veins.
Less-invasive percutaneous catheter ablation techniques have been disclosed which use end-electrode catheter designs with the intention of ablating and thereby treating focal arrhythmias in the pulmonary veins. These ablation procedures are typically characterized by the incremental application of electrical energy to the tissue to form focal lesions designed to terminate the inappropriate arrhythmogenic conduction.
One example of a focal ablation method intended to treat focal arrhythmia originating from a pulmonary vein is disclosed by Haissaguerre, et al. in xe2x80x9cRight and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillationxe2x80x9d in Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996). Haissaguerre, et al. discloses radiofrequency catheter ablation of drug-refractory paroxysmal atrial fibrillation using linear atrial lesions complemented by focal ablation targeted at arrhythmogenic foci in a screened patient population. The site of the arrhythmogenic foci were generally located just inside the superior pulmonary vein, and the focal ablations were generally performed using a standard 4 mm tip single ablation electrode.
Another focal ablation method of treating atrial arrhythmias is disclosed in Jais et al., xe2x80x9cA focal source of atrial fibrillation treated by discrete radiofrequency ablation,xe2x80x9d Circulation 95:572-576 (1997). Jais et al. discloses treating patients with paroxysmal arrhythmias originating from a focal source by ablating that source. At the site of arrhythmogenic tissue, in both right and left atria, several pulses of a discrete source of radiofrequency energy were applied in order to eliminate the fibrillatory process.
Other assemblies and methods have been disclosed addressing focal sources of arrhythmia in pulmonary veins by ablating circumferential regions of tissue either along the pulmonary vein, at the ostium of the vein along the atrial wall, or encircling the ostium and along the atrial wall. More detailed examples of device assemblies and methods for treating focal arrhythmia as just described are disclosed in PCT Patent Application Publication No. WO 99/02096 to Diederich et al., and also in the following pending U.S. patent applications: U.S. Ser. No. 08/889,798 for xe2x80x9cCircumferential Ablation Device Assemblyxe2x80x9d to Michael D. Lesh et al., filed Jul. 8, 1997, now U.S. Pat. No. 6,024,740, issued on Feb. 15, 2000; U.S. Ser. No. 08/889,835 for xe2x80x9cDevice and Method for Forming a Circumferential Conduction Block in a Pulmonary Veinxe2x80x9d to Michael D. Lesh, filed Jul. 8, 1997; U.S. Ser. No. 09/199,736 for xe2x80x9cCircumferential Ablation Device Assemblyxe2x80x9d to Chris J. Diederich et al., filed Feb. 3, 1998; and U.S. Ser. No. 09/260,316 for xe2x80x9cDevice and Method for Forming a Circumferential Conduction Block in a Pulmonary Veinxe2x80x9d to Michael D. Lesh.
Another specific device assembly and method which is intended to treat focal atrial fibrillation by ablating a circumferential region of tissue between two seals in order to form a conduction block to isolate an arrhythmogenic focus within a pulmonary vein is disclosed in U.S. Pat. No. 5,938,660 and a related PCT Patent Application Publication No. WO 99/00064.
Thermocouples have been used with prior ablation catheter to position and regulate the ablation process. A difficulties arises, however, with positioning and regulating the ablation process with one or more thermocouples where ablation occurs though an inflatable balloon, such as when the device assembly disclosed in PCT Patent Application Publication No. WO 99/02096 to Diederich et al. Thermocouples are usually mounted to the catheter shaft, and if ablation occurs at an interface between the balloon and the tissue, the thermocouples do not accurately measure the temperature because of their remote distance relative to the ablation site. Accordingly, a need exists for a temperature monitoring assembly and method to monitor catheter position, wherein at least one thermocouple is mounted on the balloon in sufficiently close proximity to the selected ablation site to provide accurate positioning information.
The present invention provides a medical device system for ablating a circumferential region of tissue in order to form a circumferential conduction block along an area where a pulmonary vein extends from a left atrium. Such conduction block may be formed in order to, for example: electrically isolate a focal source of arrhythmia in the pulmonary vein from the rest of the atrium; or connect linear lesions such that a pattern of conduction blocks may be formed to isolate a region of the posterior left atrial wall from the rest of the atrium.
One aspect of the present invention couples a position monitoring assembly to a circumferential ablation member in order to controllably position the circumferential ablation member at a desired location such that the ablation member may couple to and ablate the circumferential region of tissue. In various modes of the invention, the position monitoring assembly incorporate ultrasound sensors, pressure sensors, temperature sensors, or other sensors or combinations thereof in order to monitor the location of the ablation member relative to the tissue to be ablated. Such sensors are disposed on a delivery member (e.g., a catheter), which delivers an ablation member to the target site, and are coupled to a system that receives and displays feedback information for use in positioning the ablation member at the target site.
According to one mode, the position monitoring assembly monitors the position of the ablation member by use of an ultrasound sensor assembly that is operated in an amplitude mode (A-mode). In this mode, the ultrasound sensor assembly monitors the distance from the sensor on the catheter to the nearest wall. The distance between the ultrasonic sensor and a surrounding wall is closer when the sensor approaches or is within the vein than when the sensor is within the larger chamber of the atrium, which difference is monitor by the position monitoring assembly.
According to one aspect of this mode, an ultrasonic ablation element is also used for xe2x80x9cA-modexe2x80x9d ultrasonic sensing in order to monitor the position of the ablation element. According to another aspect, a separate ultrasonic transducer is used as a distinct element from a separate ablation element in order to provide xe2x80x9cA-modexe2x80x9d position sensing and monitoring. The separate transducer may be provided: distal to the ablation element; proximal to the ablation element; in a combination of two such separate transducers located both proximally and distally to the ablation element; or between two ablation elements.
In another aspect, a multi-mode ultrasonic sensor is used to monitor the position of an ablation element with respect to an axial centerline of the ostium. In one particular variation, a multi-mode ultrasonic sensor is used to monitor the skew angle between an axial centerline of the ablation element and an axial centerline of the ostium.
In another aspect, a multi-mode ultrasonic sensor that is used in the position monitoring assembly is constructed by disposing separate electrodes about a single piezoelectric module.
In another mode, Doppler ultrasound is used in the position monitoring assembly to ascertain the position of the catheter by measuring the velocity of blood near the catheter. Further to this aspect, blood has been observed to flow faster in the vein than in the atrium, and therefore an observed increase in the ultrasonically sensed blood velocity next to the ablation member provides indicia that the catheter has entered the vein from the atrium.
According to a further mode, an ultrasonic imaging system is used to measure the position of the catheter. In one variation, an ultrasonic imaging assembly includes an imaging sensor directly coupled to the ablation member. Other variations using ultrasonic imaging assemblies and techniques include transthoracic echo (TTE), transesophageal echo (TEE), or intracardiac echo (ICE), and the like. Desirably, these forms of ultrasonic imaging are used in combination with one or more of the other modes of position monitoring disclosed herein.
According to yet a further mode, pressure sensors are used to measure catheter position relative to the pulmonary vein ostium. A change in monitored blood pressure distal to the catheter provides indicia that the catheter has entered the vein from the atrium, for example according to known differences in the physiological pressures in such regions. Or, the pressure monitoring may be performed according to a recognized pressure change reflecting the presence of the catheter in the vein, and in particular, when an expandable member (e.g., balloon) is expanded to an occlusive profile as the ablation member enters the vein. In one variation of this mode, the pressure of the fluid within a balloon located along the ablation member is sensed.
Both modes of the position monitoring system that involve the use of Doppler and pressure sensors involve sensing physiological changes resulting from a change in the anatomic structure between the left atrial chamber and the relatively narrower pulmonary vein ostium. A clinician can determine when the ablation member is advanced. into the pulmonary vein ostium by observing a marked differential in pressure or blood velocity between these two body spaces.
In another mode, a temperature monitoring assembly and related method is used to monitor catheter position. The tissue wall of the vein changes temperature during ablation, such as when the ablation element is actuated and positioned at the desired location relative to the tissue. This change in temperature is measured with a temperature sensor positioned along the circumferential ablation member. In one particular variation of this mode, an ablation element of the circumferential ablation member is actuated before introduction of the circumferential ablation member into the pulmonary vein, such that a temperature change at the temperature sensor indicates a position of the ablation member relating to the desired ablative coupling of the ablation element to the desired tissue.
In accordance with another aspect of the present invention, feedback sensors are either attached to or used with an expandable member to sense a variety of parameters relating to the progression and efficacy of the ablation process. Such sensors desirably are used in combination with one or more of the position monitoring modes to aid in positioning and, in some applications, to determine whether contact between the ablation member and the target tissue has occurred. These sensors desirably are for either sensing temperature or mapping electrical signals, and preferably, both types of sensors are used with the ablation member.
A further aspect of the invention provides a position-sensing ablation catheter system that includes a circumferential ablation member and a position monitoring assembly that is adapted to sense the position of the circumferential ablation element relative to the circumferential region of tissue to be ablated. One contemplated feature for the delivery assembly provides a guidewire moveably engaged with a guidewire tracking member that is coupled to the circumferential ablation memberxe2x80x94advancing the guidewire tracking member over the guidewire allows the ablation element to be positioned at the desired location for ablation. According to a further feature, the circumferential ablation member provides an expandable balloon. The expandable balloon may be positioned to engage the circumferential region of tissue and thereby directly couple the ablation element to the tissue, or may be positioned to otherwise anchor the ablation element at a desired location relative to the tissue to be ablated. In either event, the position sensor is used to determine the location of the ablation member relative to the circumferential region of tissue to be ablated at the location where the pulmonary vein extends from the left atrium.
An additional aspect of the invention involves a method of positioning an ablation element relative to a circumferential region of tissue located where a pulmonary vein extends from a left atria, such as the base of the pulmonary vein itself, along the pulmonary vein ostium, or along the posterior left atrial wall and surrounding the pulmonary vein ostium.
One mode of the method involves the acts of: (1) providing a circumferential ablation member with an ablation element and that is coupled to a delivery assembly, (2) advancing the circumferential ablation member with the delivery assembly from a left atrium and toward a pulmonary vein ostium until the circumferential ablation member is positioned at a desired location such that the ablation element may be ablatively coupled to the circumferential region of tissue; and (3) using a position sensor to monitor the position of the circumferential ablation member relative to the desired location. According to one variation of this mode, the delivery assembly may provide a guidewire or guide member moveably engaged to a tracking member that is coupled to the circumferential ablation member, such that the circumferential ablation member is advanced toward the pulmonary vein by tracking the tracking member over the guidewire in the pulmonary vein.
Furthermore, the specific desired location for the ablation member that is adapted to ablatively couple the ablation element to the desired circumferential region of tissue may not be predetermined or known for a particular patient prior to positioning the ablation member according to the embodiments herein described. The system and method of the present invention therefore allows the respective anatomy of a given patient to be self defining of such desired location. The position monitoring assembly senses when the ablation member""s position is at a location that enables ablative coupling of the ablation element to a circumferential region of tissue such that the desired circumferential conduction block may be achieved.
An additional aspect of the present invention involves an ablation system comprising an ablation device assembly that includes at least one position sensor, and a position monitoring system that communicates with the position sensor. The position monitoring system desirably includes a display. The ablation device assembly includes an ablation member comprising an expandable member and an ablation element. An ablation actuator is coupled to the ablation element to selectively actuate the ablation element to form a lesion at a targeted site. In one variation, the ablation actuator comprises an ultrasonic generator that drives an ultrasonic transducer which forms at least a portion of the ablation element. In another variation, the ablation actuator includes a radio-frequency current source. The ablation system also desirably includes an expansion actuator coupled to the expandable member. In one variation, the expansion actuator includes a pressurizeable source of inflation medium.
An additional aspect of the present invention involves an ablation system comprising an elongate body with a proximal end portion and a distal end portion, means for ablating a region of tissue, and means for sensing a position of said ablation means relative to a pulmonary vein ostium.
Another aspect of the present invention includes a method for positioning an ablation apparatus in a pulmonary vein ostium, comprising using an ultrasonic sensor to measure a distance from the sensor to a tissue wall and determining a position of an ablation member with respect to the tissue wall based on a position of the ablation member with respect to the sensor.
In a variation of the positioning method of the present invention, a method is disclosed for positioning an ablation apparatus in a pulmonary vein ostium. The method comprises using a temperature sensor to measure a temperature rise produced by an ablation element and observing a time-history profile of the temperature rise as the ablation element is inserted into a pulmonary vein ostium.
Alternatively, a method for determining proper position and expansion of an expandable member in a pulmonary vein ostium is disclosed. The method comprises measuring a Doppler shift in a fluid flowing past the expandable member.